The present invention relates in general to a method and apparatus for controlling the amount of landfill gas generated within a landfill. More particularly, the present invention relates to a method and apparatus for controlling the amount of landfill gas generated within a landfill, capable of increasing a utilization efficiency of the methane gas resource to a maximum and stabilizing the landfill over a short period of time. These results are achieved by the appropriate control of the generation rate of the landfill gas containing methane generated continuously during the landfilling, degradation and stabilization processes of wastes as a main component.
Recently, with a rise in the standard of living, the generation of wastes including industrial wastes and municipal solid wastes is trending toward an increase by geometric progression. These mass-generated wastes are mostly treated by landfilling and incineration, as there is no suitable way of treating the wastes.
However, such mass-landfilled wastes need to be degraded in short period so that the landfill can be used effectively. These landfilled wastes have always a risk as an environmental pollution source until the wastes are completely degraded to be stabilized after long periods of time have lapsed. In particular, due to the eruption of contaminants, such as heavy metal, contained in landfilled waste itself from the landfill, or the infiltration of rainwater into the landfill, leachate from the landfill act as a main factor contaminating the adjacent soils or streams.
Additionally, an excess of landfill gas is generated during the degradation process of a variety of organic material contained in the landfilled wastes. This landfill gas causes serious atmospheric pollution. As the landfill gas contains, as main components, methane and carbon dioxide, it results in a greenhouse effect upon the emission into the atmosphere. Thus, the landfill gas has a problem in that acts as a direct factor to abnormal climate phenomena such as the La Nina and El Nino.
In particular, in the case where the methane contained in the landfill gas is in the amount of 50 to 60%, it is negative in view of the environmental pollution as it has an influence on the greenhouse effect to a degree of 21 times or more compared to that of carbon dioxide. However, as methane is very excellent in combustion property, an efficient technology for collecting the landfill gas is keenly demanded if taking the resource utilization aspect into consideration. Furthermore, due to the oil shock which had been encountered throughout the world in the early 1970""s, some advanced countries such as USA, Germany, etc. have begun to newly recognize, as a good quality resource, the landfill gas containing methane as its main component. At present, it has come to the stage of developing a technology put to practical use with a landfill gas treatment facility capable of collecting and treating the landfill gas by collection pipes disposed at one side of the landfill.
Generally, the landfills can be classified, depending on the landfilling method, into an anaerobic landfill, an anaerobic sanitary landfill in which a daily intermediate soil covering is carried out, a semi-aerobic landfill in which an apparatus for collection and delivery of water is disposed, and an aerobic landfill into which air can be injected. Among these landfills, the semi-aerobic landfill or the aerobic landfill is preferable in view of environmental consideration such as the generation of offensive odors, but the equipment and operation costs are excessive.
In the cases of the semi-aerobic landfill or the aerobic landfill, the content of methane, an anaerobic degradation product, in the landfill gas is relatively reduced. However, if a method capable of efficiently utilizing and controlling the landfill gas with time can be presented, the anaerobic sanitary landfill is preferable when considering all the environmental and economical aspects, such as the utilization of the waste resource. The amount of landfill gas generated with time within such landfills exhibits a great variation for each stage of a waste landfilling process, a waste post-landfilling process and a landfilling stabilization process, depending on a variety of factors such as the waste character, the landfilling method and the natural conditions. These stages have been generally progressing over a period of time for about 20 years. This landfill gas generation amount shows a maximum value at a point of time of about one year to three years after the completed landfilling, as shown in FIG. 3 showing a curve of landfill gas production rate in a common landfill.
Therefore, for an efficient extraction, collection, and utilization of an entire amount of the landfill gas generated within the landfill, a utilization facility involved needs to be designed and constructed with respect to a maximum generation amount of the landfill gas. However, such design and construction has many problems when considering the economical aspect, and thus can be applied only to the limited landfill facility of a special scale. As a result, only about 30% to 50% of the capable landfill gas generation in the landfill is utilized, and the remainder is incinerated or escaped into the atmosphere.
Taking such a problem into consideration, studies are progressing to artificially controll the anaerobic condition in the landfill at the landfilling process, thereby increasing a generation of the landfill gas. The activation of the anaerobic condition in the landfill also enables the landfill gas utilization facility to be designed at a reasonable capacity and to be used for an extended period of time, and also to be shortened in a recovery term of its investment cost. Typically, in Korean Patent Application No. 97-56300, there is disclosed a landfill process comprising the steps of landfilling wastes between vertically built banks, and graveling the wastes surface to enable the ventilation therethrough. The disclosed process further includes the subsequential steps of disposing pipelines for injecting leachate amid the gravel, covering the gravel with a sealing sheet at just slightly higher above the gravel, and then soil-covering.
In the above described patent application, the leachate effluent from the landfill is simply recycled to be injected into the final cover of the landfill. This is advantageous in that the amount of generated leachate is significantly reduced. Another advantage is in that an aerobic condition at an initial stage of the landfilling process is weakenened while activating the anaerobic condition, such that the amount of generated methane gas contained in the landfill gas at an initial stage of the landfilling process can be somewhat increased.
However, the technology described in the patent application is to facilitate the generation of methane at an initial stage of the landfilling process, depending only on the simple recycling of the leachate. Since, in the above application, there is no consideration for other factors facilitating gas generation such as pH and temperature within the landfill, it has a limitation in maintaining the amount of generated gas at a constant level throughout an entire duration of the landfilling process, the post-landfilling process and the landfilling stabilization process by suitably controlling a phenomenon in that the amount of the generated landfill gas is rapidly increased at the completed landfilling and is rapidly decreased at the landfilling stabilization process. Therefore, the above prior application is problematic in that it is difficult to determine the reasonable scale of the facility for utilizing landfill gas and also an efficiency for utilizing landfill gas is greatly decreased.
It is therefore an object of the present invention to provide a method and apparatus of controlling the amount of landfill gas generated within a landfill capable of designing facilities necessary for the recovery of the landfill gas, such as purification and power generation facilities, at a reasonable scale. This method and apparatus thus enables the cost of the investment in the facilities to be recovered over a short period of time, the utilization efficiency of the landfill gas resource to be maximized, and also the landfill to be stabilized over a short period of time. Such an object is achieved by suitably monitoring and controlling a variety of conditions of the recycling leachate for every stage of a landfilling process, a post-landfilling process and a landfilling stabilization process, such that the amount of the landfill gas generated is kept as constant as possible throughout all these processes.